Abstract : According to Burkitt-s hypothesis, dietary fibres may protect against the development of colorectal cancer. In rats, studies have shown that only butyrate-producing fibres are protective. In parallel, in humans, non-steroidal anti-inflammatory drugs, which target cyclooxygenases, have been shown to display a protective effect against colorectal cancer. Among them, COX-2-selective inhibitors which present less side effects than non-selective agents, are promising as chemopreventive agents. Our aim was to analyse the effect of an association between butyrate-producing fibres and the COX-2 inhibitor on the development of aberrant crypt foci ACF in rats. Fisher F344 rats were fed with 1 a standard low fibre control diet; 2 the standard diet supplemented with 1500 ppm celecoxib; 3 a diet supplemented with 6% fructo-oligosaccharide FOS; and 4 a diet with both celecoxib and FOS. Three weeks later, the rats were injected twice with azoxymethane and the number of ACF was determined 15 weeks later. In the control group, $43.8 \pm 6.4$ ACF were found. This number was not significantly modified by the addition of FOS or celecoxib alone to the diet. However, the association of FOS and celecoxib resulted in a 61% reduction in the number of ACF $P < 0.01$. The number of aberrant crypt per foci was also reduced. Thus, although no significant effect of celecoxib or FOS alone was identified, the association of butyrate-producing fibre and celecoxib was effective in preventing the development of ACF. This preliminary study argues for a strong protective effect of such an association which deserves further studies.